Many studies in the medical sciences involve the measurement of several aspects on each individual on repeated occasions. Often, scientific interest is in studying the inter-relationships, which might be causal, between measurements. Graphical modelling provides a strategy for translating substantive hypotheses about causal relationships into a statistical model. Further, scientifically relevant results from the statistical analysis of the data can be communicated through an intuitively natural graphical representation of the fitted model. The aim of this project is to make use of recent developments in the area of graphical models to advance research in medical contexts, including developmental psychology, neuropsychology and brain ageing. This project will focus on two areas: 1) assessment of decline in the cognitive functions of Alzheimer‘s patients and 2) identification of particular executive and social-cognitive problems associated with focal epilepsy in children. Evaluation of data to study development and deterioration of cognitive performance in individuals requires the consideration of latent variables to represent qualities of individual subjects that cannot be measured directly. Often the directly observed data are qualitative, for example success or failure on a psychometric test. A major goal is to develop a flexible modelling strategy for data of this kind.